The light emitting elements in conventional bulbs (the filament of an incandescent bulb or the fluorescent material in a fluorescent bulb) are extremely bright and emit light in every direction. In many applications, directed lighting is preferred, for example with spotlights, floodlights, or track lighting. For these applications, traditional lighting devices such as incandescent or fluorescent light bulbs typically require reflectors or lenses to direct the light output. For example, desk, table, floor and ceiling lamps conventionally use shades to reflect light to the ceiling or floor to provide indirect lighting suitable for use in a home or office environment. Spotlights or floodlights place the lighting element within a curved reflector to direct the light. Thick glass conventional lenses and fresnel lenses are often employed to both refractively direct the light emitted and to seal the lighting elements. These reflectors and lenses are expensive, may be heavy, and take considerable space.
Solid-state lighting devices made of light emitting diodes are increasingly useful for applications requiring robustness and long-life. For example, solid-state LEDs are found today in automotive applications. These devices are typically formed by combining multiple, small LED devices providing a point light source into a single module together with glass lenses or reflectors suitably designed to direct the light as is desired for a particular application; see for example, WO99/57945, published Nov. 11, 1999. These multiple devices are expensive and complex to manufacture and integrate into single illumination devices.
Organic light emitting diodes (OLEDs) are manufactured by depositing organic semiconductor materials between electrodes on a substrate. This process enables the creation of light sources having an extended light emitting surface area on a single substrate. The prior art describes the use of electro-luminescent materials as adjuncts to conventional lighting; see for example U.S. Pat. No. 6,168,282, issued Jan. 2, 2001 to Chien. In this case, because of the limited light output from the electro-luminescent material, it is not useful for primary lighting.
EP1120838A2, published Aug. 1, 2001 describes a method for mounting multiple organic light emitting devices on a mounting substrate to create a light source. However, the light source is not directed.
There is a need therefore for an improved OLED lighting apparatus for directed illumination having a simple construction that provides a highly integrated and robust light.